The present invention relates to a helicopter rotor. In particular, the present invention relates to an articulated rotor on which each blade is connected to a center hub on the rotor by means of a fork, in turn, connected in articulated manner to a center hub on the said rotor.
On articulated rotors of the aforementioned type, each blade oscillates, in relation to the hub and about the said articulated joint, both vertically, due to lift and in a plane perpendicular to the hub plane, and horizontally in the hub plane, due to inertia and drag. Known rotors of the aforementioned type are generally provided with limiting devices for maintaining vertical and horizontal oscillation angles within a relatively limited range, when the speed of the rotor is below a given set value.
In more detail, limiting devices are known to be employed comprising rocker arms mounted on the said fork or hub and designed to move, due to centrifugal force, between a normal idle position, wherein the said rocker arms are designed to cooperate with contact surfaces on the said hub or, respectively, on the said fork, for limiting the said oscillation, and an operating position wherein the blade is free to oscillate.
The main drawback on articulated rotors with limiting devices of the aforementioned type is that, in addition to the said vertical and horizontal oscillation, the said articulated joint connecting the fork and hub also allows the blade to turn and change pitch about its own axis. As such pitch-change rotation obviously results in displacement of the said contact surfaces and the paths of the respective rocker arms, contact between the said rocker arms and respective contact surfaces is impaired, thus resulting in rapid wear and reduced efficiency of the said limiting devices.
This is extremely dangerous, especially as regards vertical oscillation control, in that, whereas horizontal oscillation is kept under control at all times by means of hydraulic dampers between the blade and hub, low-speed vertical oscillation is generally limited solely by the said rocker arms, any inefficiency of which may result, especially during take-off and due to both wind and "ground effect", in a sharp upward sweep of the blades and consequent overturning of the helicopter.